Locate and parameterise objects on an image frame
It is important the frame supplied to the program is clean of all defects and has a flat background. The data values should be in the range 0 to 32766.
If this is true then all objects which are connected at the threshold level are examined to see if they comprise more than one object at a higher level. If this is so the signal in the object is apportioned between the components and the parameters calculated accordingly.
If this is false the image parameters are calculated for those objects which are connected at the threshold level. [TRUE]
If this is true then during the full surface modelling procedure the background is allowed to vary, over a blend of objects, in addition to the object’s position and intensity, to best fit the data.
If this is false then the background is held constant during the full surface modelling procedure. [FALSE]
If this is true a fixed sized circular aperture is used. If this is false the total intensity is estimated from the curve of growth using elliptical apertures that match the shape of the objects. [FALSE]
If this is true the program examines a difference map of the raw data minus the fitted profiles to see if any other objects are present. The fitting procedure is repeated until a stable solution is reached. This option is very time consuming.
If this is false the program uses the images found from an isophotal analysis as a basis for the profile fitting, and does not examine the difference map for additional objects. Some objects may be merged together if they are too close, or if the fit is better in a least squares sense. [FALSE]
If this is true then negative going images (those below the background level) will be searched for, as well as the usual positive going images. The same threshold and minimum connectivity is used for both directions. If the negative going images are assumed to be due to random fluctuations in the background then the number of negative images will indicate the proportion of false detections that may be present amongst the positive going images. Only isophotal analysis is applied to the negative images. Negative going images are indicated in the results file with minus signs in the first field.
If this is false then only positive going images are sought. [FALSE]
If this is true then the data is smoothed with a 3 x 3 Hanning filter before the isophotal analysis is performed. This is useful if the deblending is fragmenting the data too much. The object parameters are calculated using the unsmoothed data.
If this is false the raw data is used for the object searches. [FALSE]
MINPIX = _INTEGER (Read)
If this is true the whole data array is analysed. If this is false the pixel coordinates defining a subset of the data to be analysed is requested. [TRUE]
The data input to PISAFIND can be any size (within system limits), however, the length of the first dimension is restricted to less than 10241 pixels.
The output in the RESULTS file contains the following information:
Column | Name | Description |
1 | INDEX | Index number of object. |
2 | XPOS | X position of object in pixels. |
3 | YPOS | Y position of object in pixels. |
4 | INTENSITY | Integrated intensity of object. |
5 | NPIX | Number of pixels above threshold. |
6 | PEAK | Peak intensity of object in one pixel. |
7 | ELLIPT | Ellipticity of object. |
8 | ANGLE | Orientation of object, anti-clockwise from y-axis. |
9 | SXX | Second moment of data in x. |
10 | SYY | Second moment of data in y. |
11 | SXY | Cross moment of data in x and y. |
The output in the RESULTS file contains the following information:
Column | Name | Description |
1 | INDEX | Index number of object. |
2 | A1 | Number of object pixels within threshold. |
3 | A2 | Number of object pixels within i=2 threshold. |
4 | A3 | Number of object pixels within i=3 threshold. |
5 | A4 | Number of object pixels within i=4 threshold. |
6 | A5 | Number of object pixels within i=5 threshold. |
7 | A6 | Number of object pixels within i=6 threshold. |
8 | A7 | Number of object pixels within i=7 threshold. |
9 | A8 | Number of object pixels within i=8 threshold. |
The SIZES thresholds are determined by the equation.
where It
is the threshold intensity.